Adding Bones and Attaching Vertices

Difficulty of this task differs from model to model, but since our model has only 2 limbs and the limbs are made from solid and sperate parts, it will be very easy to do and easy to understand. Let's start.

Bone Animation

As I mentioned earlier, the skeleton consists of severeal bones, and vertices of the model will be attached to that bones. And instead of moving every vertex for each frame of animation, we will assign them to bones and rotate these bones. This may look like an extra step opposed to vertex animation, but in complex models it is alot easier to animate this way. Nearly all big game titles uses bone animation for characters,monters and othervariety of models.

We will first build the sekeleton then attach vertices to bones.

Building the Skeleton

First, go to Bone Mode by clicking the Bone Mode icon from the toolbar. The bone toolbar at the bottom of the screen that is normally inactive will become enabled. Grayed out buttons will become colored.

We will be using only fisrt two buttons for this tutorial to keep it simple. Click on the first button, Create Bone from the bone toolbar. And then click in the place where the hinge of the robot's legs should be, from the side view:

A circle will appear. This is your first bone! If your circle is too big or too small you can change it's size by going to File -> Preferecens -> Misc and changing the Bone Size value.

Make sure it is in the middle of the two legs from the front view, if it's not move it to the middle by using the move tool:

By default it should be red, that means it is selected. When you add another bone while a bone is selected, the selected bone and the newly created bone will be connected to each other. We will generally want to create a full conntected sekeleton. When you rotate a bone, all connected bones will rotate accordingly. While you are still on the front view, click on the center of one of the legs:

A new bone connected to the first bone is created! Now get to the side view and create this bone structure (You only need 2 more clicks to do this.) :

You see how the one of them is blue and others have yellowish color? Yellow ones are normal, unselected bones, the red one is our selected bone. And the blue color indicates the connection to "parent" bone. It means if you rotate the bone at the other edge of the blue colored part, your currently selected bone will also rotate. This can sound kind of confusing, but it will make great sense in 10 minutes.

Now select the first bone again:

The color of the bones of the leg is changed, it's white by default but i changed it to green since it's a little hard to see from the edges. This indicates the "child" bones, it means that if you rotate this bone, all the green bones will rotate too.

Now that our first bone is selected again, add a bone for other leg this time:

Now, you are going to repeat the same steps for the other leg from side view. There is bones of the first leg on the view, but no problem! You can either hide them or use them as helpers for your new leg! Just click on the center of the bone circles of the first leg(watch the front view while doing that), and the bones for your new leg will be added.

Our finished skeleton:

We have a skeleton, skeleton alone does not mean much. Bones do not know which vertices they should move with themselves. We are now going to tell bone which vertices they should move.

Attaching vertices to bones

Again complexity of this task changes from model to model, but since our robot model has very few and only solid parts it will be both easy to do and understand.

If you are not already in Bone Mode, switch to Bone Mode. Then from the bone toolbar click on the Apply Vertices Mode button.

Now, you should be seeing both vertices and bones in your viewports. Here is how you assign vertices to bones:

First, select the feet joint of one of the legs as shown above. While nothing is selected you can click on bones(joints) to select them.While a bone is selected:

Single clicking on vertices or drawing a selection box around vertices by single clicking an empty place and dragging will select vertices and
Double-clicking to an empty place will deselect the bone. While no bone is selected, you cannot select vertices.

Thet select the all vertices of the according feet as shown above. Quick Tip! An easy way to that: Select only on single vertex of the feet and click on the Select Connected button. Also make sure you did not selected wrong vertices by checking your selection from other views:

Nice! Looks like I only selected the vertices of the feet. If you are sure that you selected a bone and correct vertices to attach to it, click on the Apply Vertices button from the bone toolbar.

Vertices will get assigned to the bone and their color will change. The adges that will be affected of movement and rotation of that bone will also change color. If you figure out you accidentally attached vertices you did not wanted to, select these vertices and click on Remove Vertices button. This will de-assign the selected vertices from the bone and vertices will change back to their original color. Now go ahead and select the knee joint. Note that you can deselect currently selected bone by double clicking on an empty space in viewport.

You will notice that the color of the vertices attached to feet bone will have a different color. This indicates that these vertices are already attached to some other bone other than the currently selected one.

Tip: Already attached vertices cannot be attached to another bone, so selecting them while working for other bone won't change the bone they are assigned to. For instance if i select the vertices shown below:
Note to users with other 3d animation software experience: The Acknex Engine DOES support vertex weigths(assignin vertices to multiple bones). This is just the limitation of the MED, in which you can only assing a vertices to a asingle bone.

And assign them to the knee joint, i will get this:

This can come pretty useful when working with more complex models. On a side note, while working from side view, make sure you are not selecting the vertices of the other leg. Double check your selection from other viewports and remember that you can substract vertices from your selection by holding [Shift] and click on the vertices you want to deselect.(Selection box will also work for deselecting with [Shift])

Now attach the vertices of the upper leg by using the methods explained above.

One of the legs is finished. Repeat all steps above for the other leg.

Then attach the remaning body vertices to the bone in the middle of the skeleton.

Done! We attached all vertices to bones and we are ready to animate the model!